Hot dip aluminum coating



United States Patent 3,000,756 HOT DIP ALUMINUM COATING John Logan,Pittsburgh, Pa., assignor to The Wean Engineering Company, Inc., Warren,Ohio, a corporation of Ohio No Drawing. Filed Aug. 9, 1957, Ser. No.677,214 18 Claims. (Cl. 117-51) This invention relates to the coating ofmetallic objects with an adherent ductile coating of aluminum. It isparticularly useful in coating steel wire, steel strip and the like withaluminum.

It has long been customary to coat steel and other base metals withcoating metals for the purpose of protecting the base metal againstcorrosion or to provide other surface qualities not inherent in the basemetal. Such metals have been applied by hot dip processes, byelectrolytic plating, or by rolling slabs of different metals together.To the best of my knowledge, all present methods of coating a basemetal, such as steel, with aluminum have marked disadvantages in thatthey require a protective atmosphere as well as the installation ofexpensive equipment. Hot dip processes have been employed to depositaluminum on steel, but even in the presence of various fluxes, they havebeen only partially successful. The coatings heretofore produced by thehot dipping of metallic objects in aluminum have produced coatings whichare brittle. Some, for example, adhere satisfactorily only after passingthe coated metal through a rolling mill. Such coatings do not adheresatisfactorily to wire. In many instances, the fluxes which have beenemployed for hot dipping in aluminum are poisonous, corrosive, orotherwise extremely diflicult to handle.

I provide a flux selected from the group comprising phosphorus andcompounds of phosphorus with sulphur. It is essential that the flux notcontain oxygen in order to produce satisfactory results. I prefer toemploy phosphorus free of oxygen but find that compounds of phosphorusand sulphur also produce satisfactory results.

A few examples will serve to illustrate my invention. Red phosphorus wasapplied to various steel specimens. For example, the phosphorus wasreduced to a fine powder and then suspended in water. The phosphorus andwater were then sprayed on the specimens. Upon evaporation of the water,a fine coating of phosphorus remained adhering to the metal. Afterapplication of the phosphorus, the metal was dipped in a pot of moltenaluminum for a preferred time of two or three seconds under thefollowing conditions:

Tempera- Dipping Example Flux ture of Al, Time,

1*. seconds 1 Powdered P4 in hot water 1, 290 5 sprayed on steel strip.Powdered P4 in cold water 1, 290 3 sprayed on steel strip. Powdered P4in hot Water 1. 290 3 sprayed on steel strip.

Alternatively, finely divided phosphorus may be suspended in an organiccarrying agent such as alcohol.

Patented Sept. 19, 1961 ice Tempera- Dipping Example Flux ture of Al,Time,

F. seconds 8 Powdered P4 rubbed on 1, 260 3 steel strip with a cloth. 9Powdered P4 rubbed 0n 1, 290 3 steel Wire with a cloth.

When phosphorus is applied to clean mild steel in the manner described,a ductile and highly adherent coating of aluminum is produced. Forexample, when ordinary steel wire is coated in accordance with theinvention herein, repeated flexing of the wire will not break orseparate the aluminum coating from the steel until the steel itself isat the point of rupture from work hardening resulting from the repeatedflexure. As noted above, the coating is apparently less ductile if thetemperature of the aluminum bath and the dipping time are increased.

Compounds of phosphorus with sulphur have also been employed as fluxeswith satisfactory results. For example, phosphorus pentasulfide, P 8 hasbeen employed in the same manner described for red phosphorus and hasproduced a satisfactory coating. The following examples areillustrative.

'Ie'mpera- Dipping Example Flux ture of Al, Time,

F. seconds 10 Powdered P255 in methyl- 1, 260 3 ene chloride sprayed onsteel strip. 11 Steel strip dipped in carbon 1, 330 3 disulfidesuspending P285. 12 P285 rubbed on steel strip 1, 290 3 with a cloth. 13Powdered P585 rubbed on 1, 290 6 steel Wire with a. cloth dipped incarbon disulfide.

In the same manner, phosphorus trisulfide, P 8 has been employed toproduce a useful product. The coating has, however, been lesssatisfactory than that produced using red phosphorus or phosphoruspentasulfide. The following example is noted as producing a reasonablysatisfactory coating.

Tempera Dipping Example Flux ture of Al, Time,

F. seconds 14 Steel strip dipped in carbon 1, 310

disulfide in which powdered P43 was suspended.

from the group consisting of phosphorus and compounds of phosphorus withsulphur, and then immersing the metal in molten aluminum.

2. The product of the process of claim 1.

3. The method of coating a ferrous metal with aluminum which comprisesfluxing the metal with a member selected from the group consisting ofphosphorus and compounds of phosphorus with sulphur, and then immersingthe metal in molten aluminum.

4. The method of coating a ferrous metal with aluminum which comprisesfluxing the metal with red phosphorus, and then immersing the metal inmolten aluminum.

5. The product of the process of claim 4.

6. The method of coating a ferrous metal with aluminum which comprisesfluxing the metal with P 8 and then immersing the metal in moltenaluminum.

7. The product of the process of claim 6.

8. The method of coating 21 ferrous metal with aluminum which comprisesfluxing the metal with P 8 and then immersing the metal in moltenaluminum.

9. The product of the process of claim 8.

10. The method of coating a metal with aluminum which comprises cleaningthe metal, coating the surface of the metal with a flux selected fromthe group consisting of phosphorus and compounds of phosphorus withsulphur, immersing the metal in a bath of molten aluminum and thenwithdrawing it therefrom.

11. The method of coating a ferrous metal with aluminum which comprisescleaning the ferrous metal, coating the surface of the metal with a fluxof red phosphorus, immersing the metal in a bath of molten aluminum andthen withdrawing it therefrom.

12. The product of the process of claim 11.

13. The method of coating a ferrous metal with aluminum which comprisescleaning the ferrous metal, coating the surface of the metal with a fluxof P 8 immersing the metal in a bath of molten aluminum and then withdrawing it therefrom.

14. The method of coating a ferrous metal with aluminum which comprisescleaning the ferrous metal, coating the surface of the metal with a fluxof P 8 immersing the metal in a bath of molten aluminum and thenwithdrawing it therefrom.

15. The method of coating a metal with aluminum which comprises mixing aliquid with a flux selected from the group consisting of phosphorus andcompounds of phosphorus with sulphur, spraying the mixture on saidmetal, allowing the liquid to evaporate and then immersing the metal ina bath molten aluminum and withdrawing it therefrom.

16. The method of coating a metal with aluminum which comprises mixingwater and a flux selected from the group consisting of phosphorus andcompounds of phosphorus with sulphur, spraying the mixture on saidmetal, allowing the water to evaporate and then immersing the metal in abath of molten aluminum and withdrawing it therefrom.

17. The method of coating a metal with aluminum which comprises mixingalcohol and a flux selected from the group consisting of phosphorus andcompounds of phosphorus with sulphur, spraying the mixture on saidmetal, allowing the alcohol to evaporate and then immersing the metal ina bath of molten aluminum and withdrawing it therefrom.

18. The method of coating 21 ferrous metal with aluminum which comprisesmixing water and a flux of powdered red phosphorus, spraying the mixtureon the metal, allowing the water to evaporate and then immersing themetal in a bath of molten aluminum and withdrawing it therefrom.

References Cited in the file of this patent UNITED STATES PATENTS750,511 Wherry Jan. 26, 1904 750,512 Wherry Jan. 26, 1904 1,456,274 KeepMay 22, 1923 1,501,293 Staack July 15, 1924 1,910,385 Fisher et al May23, 1933 'UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo, 3,000,756 September 19 196 John E Logan It is hereby certified thaterror appears injzhe above numbered patentrequiring correction and thatthe said Letters Patent should read as "corrected below.

Column 2 third table thereof, column 3,, line .1 thereof, insert 3column 4 line 10 after "bath" insert of Signed and sealed this 13th dayof February 1962'o (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. THE METHOD OF COATING A METAL WITH ALUMINUM WHICH COMPRISES FLUXINGTHE METAL WITH A MEMBER SELECTED FROM THE GROUP CONSISTING OF PHOSPHORUSAND COMPOUNDS OF PHOSPHORUS WITH SULPHUR, AND THEN IMMERSING THE METALIN MOLTEN ALUMINUM.